Motilityandtoneα2,β2Decrease + Increase+++ Sphinctersα Contraction(usually)+ Relaxation(usually)+ SecretionInhibition(?)Stimulation+++ Gallbladder and Ducts Relaxation+ Contraction+
Motilityandtoneα Increase(usually)Increase(?)Uterus α,β2Pregnant:contraction(α);Variable nonpregnant:relaxation(β)Sex Organs, Male α Ejaculation+++ Erection+++ + Generalizedsecretion+++ Spleen Capsule α,β2Contraction+++;relaxation+ —
Adrenal Medulla —SecretionofepinephrineandnorepinephrineLiver α,β2Glycogenolysis,gluconeogenesis β2Increasedsecretion+ —Fatcellsα,β1Lipolysis
FromGoodmanLS,GilmanA.The Pharmacological Basis of Therapeutics. 6thed.NewYork:Macmillan;1980.aAlongdash(—)signifiesnoknownfunctionalinnervation.bResponsesaredesignated+ to+++ toprovideanapproximateindicationoftheimportanceofadrenergicandcholinergicnerveactivityincontrolofthevariousorgansandfunctionslisted.cDilationpredominatesinsitubecauseofmetabolicautoregulatoryphenomena.dCholinergicvasodilationatthesesitesisofquestionablephysiologicalsignificance.eOvertheusualconcentrationrangeofphysiologicallyreleasedcirculatingepinephrine,aβ receptorresponse(vasodilation)predominatesinbloodvesselsofskeletalmuscleandtheliver,andanα receptorresponse(vasoconstriction)predominatesinbloodvesselsofotherabdominalviscera.Therenalandmesentericvesselsalsocontainspecificdopaminergicreceptors,activationofwhichcausesdilation,buttheirphysiologicalsignificancehasnotbeenestablished.fThesympatheticcholinergicsystemcausesvasodilationinskeletalmuscle,butthisisnotinvolvedinmostphysiologicalresponses.gIthasbeenproposedthatadrenergicfibersterminateatinhibitoryβ receptorsonsmoothmusclefibersandatinhibitoryα receptorsonparasympatheticcholinergic(excitatory)ganglioncellsoftheAuerbachplexus.hDependsonthestageofthemenstrualcycle,theamountofcirculatingestrogenandprogesterone,andotherfactors.iPalmsofthehandsandsomeothersites(“adrenergicsweating”).jThereissignificantvariationamongspeciesinthetypeofreceptorthatmediatescertainmetabolicresponses.
β receptor activity is controlled in a number of ways. It can be antagonized by the action of α1 receptors. The β receptors can also be desensitized by phosphorylation with prolonged exposure to agonists. Regulation of β receptor numbers represents a third control mechanism. For example, β receptor numbers can be decreased by being internalized. Alternatively, β receptor numbers can be increased (upregulated) in certain circumstances: for example, after denervation. Note that the number of α receptors is likewise regulated.
In addition to releasing norepinephrine, sympathetic postganglionic neurons release neuropeptides such as somatostatin and neuropeptide Y. For example, cells that release both norepinephrine and somatostatin supply the mucosa of the gastrointestinal tract, and cells that release both norepinephrine and neuropeptide Y innervate blood vessels in the gut and the limb. Another chemical mediator in sympathetic postganglionic neurons is adenosine triphosphate (ATP).